Here is further evidence that local metabolizm of 1,25-dihydroxyvitamin D
(active form of vitamin D) at the cellular level is different than what is found in your blood serum:
From my point of view, I am taking as much Vitamin D3 (cholecalciferol) to the estimated lowest observed adverse effect level (LOAEL) while monitoring my calcium level to be sure that I do not become hypercalcemic.
What I am taking is 40,000IU/day. The LOAEL is described in this paper:
So, I have been on this dosage for over four months and feel beter than I have ever felt since I became sick (no relapses).
The study below also brought subjects to this high of a dose without becoming hypercalcemic:
So, your doctor will tell you that taking this much Vitamin D will cause you to become hypercalcemic, but I don't believe it.
I think that the future study of clinical trials will probably be done with Vitamin D analogs, because these can be patented and proclaim the benefits of not causing hypercalcemia: